The present invention relates generally to the field of integrated circuits and, in particular, to detecting and configuring the required polarity of a circuit pin.
An integrated circuit or xe2x80x9cchipxe2x80x9d is generally installed or mounted on a system board which is ultimately installed in an end product. Commonly, an integrated circuit may be purchased for use in several (or many) different end products, often by different manufacturers. It will be appreciated that it may be impractical to use separate chip designs for similar applications. However, in the past, it has also been impractical to automatically modify chips so as to function with a variety of different system boards.
For example, audio devices such as DVD units and audio/video (A/V) receivers include a digital audio integrated circuit having, among other functional components, a digital-to-analog converter (DAC) for outputting an analog audio reproduction of a digital signal. The integrated circuit is mounted on a system board which generally includes a mute circuit to disable the analog audio output during unit power-on, reset or other predetermined events. Absent such mute, the listener would hear clicks and pops which are both distracting to the listener and potentially damaging to the audio device or speakers. And, even if only 0s are input into the DAC in an attempt to reduce the noise, clicks and pops may still be generated downstream from the DAC, especially as there may be some brief, but finite, time delay after the 0s begin to be input to the DAC.
FIGS. 1A-1D are examples of mute circuits commonly used on system boards. The circuits of FIGS. 1A and 1C are activated when the mute signal (actually the inverted mute signal) to the xe2x80x9cmute nodexe2x80x9d is in a low state, driving the mute node to ground; these circuits are said to have an xe2x80x9cactive low mutexe2x80x9d. In contrast, the circuits of FIGS. 1B and 1D have an active high mute and are activated when the control signal to the mute node is in a high state.
The mute circuit is activated by mute driver circuitry on the audio chip which, in turn, is enabled by a mute_control signal 202. FIG. 2 is an illustration of a typical prior art mute driver circuit 200. As will be understood, when the mute_control signal 202 is in a low state, transistor M0 is off and M1 is on, driving the mute node 204 high. And, when the mute_control signal 202 is in the high state, transistor M0 is on and M1 is off, driving the mute node 204 low. Depending upon whether the particular mute circuit on the system board is active high or active low, the signal to the mute node 204 must either be high or low. Consequently, the designer of the audio chip must either know in advance with which type of mute circuit the chip will be used and make available the appropriate chip or the system board designer must decide in advance which chip will be used and conform the mute circuit to the chip (and then be limited as to second or future sources of the chip). Alternatively, the chip may be designed with configurable polarity. However, configurable polarity requires either an extra and dedicated pin or a register which can be set through a control port whenever the chip goes through a power-on or reset. One disadvantage to using a register is that there may still be a delay after the chip exits the reset state until the register is configured. During this time the mute node may be in the unmute state, resulting in the undesirable clicks and pops which were to be eliminated.
Consequently, there remains a need for an integrated circuit having an inexpensive and efficient method for detecting the type of circuitry to which it is connected and having the ability to automatically configure itself with the appropriate polarity.
The present invention provides an integrated circuit mountable on a system board used, for example, in a digital audio device (such as a DVD or A/V receiver). The integrated circuit includes a digital-to-analog converter, possibly in conjunction with a CODEC, and the system board may include circuitry to, for example, mute the analog output of the device under certain predefined conditions. Because it may not be known in advance by the designer of the integrated circuit whether the circuit is activated by a signal in a high state (polarity) or a low state, the integrated circuit further includes a detector which detects and stores the required polarity (although it will be appreciated that certain of the components of the detector may also be placed off-chip). When it is necessary for the circuit to be activated, the detector provides a signal of the correct polarity.